Epoxy molding compounds have found wide use as encapsulants of semiconductor devices such as integrated circuits, transistors and diodes, passive devices and other electronic components. Such encapsulants contain an epoxy, a hardener, a catalyst, a mold release agent, usually a filler, usually a colorant and sometimes a coupling agent. Exemplary formulations of these ingredients are described in U.S. Pat. No. 4,042,550 to Tuller et al., 4,034,014 to Curtis, Jr. et al., 3,849,187 to Fetscher et al., 3,862,260 to Sellers et al., 3,789,038 to Curtis et al. and 3,280,216 to Partansky et al. Such compositions are generally classified by the type of hardener, with phenol-derived and substituted phenol-derived resin, carboxylic acid anhydride and amine hardeners being most common. Frequently, the molding compounds are highly filled (over 50% filler by weight), but for some applications low filler compositions or even unfilled compositions may be used.
In recent years, requirements of electronic industries have necessitated flame retardant grades of these epoxy molding compounds. Additives to improve the flame retardancy, as measured for example by UL-94, have been proposed including halogenated compounds, certain transition metal oxides and hydrated alumina. Unfortunately many good flame retardant additives detract from the compatibility of the encapsulant with semiconductor devices at high temperatures. In a copending application of Robert K. Rosler, U.S. Ser. No. 813,201, filed July 5, 1977, a filled epoxy novolac molding compound is described with a synergistic combination of antimony trioxide and a reactive halogenated organic compound as flame retardant. Similarly, U.S. Pat. 4,042,550 describes epoxyanhydride molding compounds with secondary fillers including antimony trioxide or antimony tetraoxide and, in flame retardant types, halogenated compounds. While such a flame retardant combination provides good flame retardance and satisfactory compatibility on electronic devices, a need still exists for flame retardant epoxy molding compounds of all types with improved compatibility.